Conventionally, in a filtration process of liquid for general industrial use such as cooling water for various apparatuses or process liquid, a filtration process of oil such as lubricating oil and diesel fuel oil, and a filtration process of gas and the like of various raw materials for use in a chemical plant and the like, various filter apparatuses are used for the purpose of trapping and removing fine particles, dust, and the like contained therein.
When filtration is performed by the filter apparatus for a long time, solid matter, accreted dust, and the like trapped on a filter element accumulate on the filter element, so that resistance of a fluid flowing from an inside to an outside of the filter element increases, and this ultimately makes the fluid to be filtered (target fluid) difficult to filter. In order to cope with this problem, for example, a process called “backwashing,” in which a fluid is made to pass through the filter element in a reverse direction of a filtering direction to remove trapped matter adhering to the filter element, is carried out periodically to restore filtering performance of the filter element.
The abovementioned backwashing process is effective. However, there may be a case in which the trapped matter adhering to the filter element is not removed completely and remains. In this case, even with repeated backwashing, the resistance of the fluid flowing from the inside to the outside of the filter element increases, and the target fluid becomes difficult to be filtered. In particular, as in a case of filtration of liquid, when accreted dust, dust covered with highly adhesive materials, and the like firmly adhere to a surface of the filter element, it is difficult to restore filtering performance of the filter element only by the backwashing making the fluid pass through the filter element in the reverse direction of the filtering direction. Among other things, a filter apparatus which uses a filter element having a pore size of less than 100 μm has such a tendency.
In order to cope with this problem, there was proposed a filter apparatus for restoring filtering performance of a filter element. As such a filter apparatus, there is proposed a filter apparatus including a housing which surrounds and seals a cylindrical filter, a raw-water pressure and supply unit which pressurizes and supplies raw water to a raw water chamber located inside the filter, a discharge unit which discharges filtrate from a filtrate chamber located outside the filter, an intake nozzle which is disposed in the raw water chamber and has an opening facing an inner surface of the filter, a wash water discharge unit which is connected to the intake nozzle and discharges drawn used wash water to the outside of the raw water chamber, a suction control unit which controls the wash water discharge unit to thereby control suction of the used wash water drawn through the intake nozzle, a nozzle moving unit which moves the intake nozzle along the inner surface of the filter, a backwash nozzle which is disposed in the filtrate chamber in a position opposed to the intake nozzle and through which backwash water is supplied, a backwash water supply unit which pressurizes and supplies the backwash water to the backwash nozzle, and a backwash nozzle moving unit which moves the backwash nozzle in synchronization with the intake nozzle (for example, refer to Patent Document 1).